Furan and related compounds are useful starting materials for industrial chemicals for use as pharmaceuticals, herbicides, stabilizers, and polymers. For example, furan is used to make tetrahydrofuran, polytetramethylene glycol, polyether ester elastomers, and polyurethane elastomers.
Known transition metal catalyzed, vapor-phase processes to produce furan by decarbonylation of furfural are limited by either the selectivity or lifetime of the supported catalyst. The conversion of furfural to furan is complicated by the tendency to form polymeric or carbonizing byproducts which foul the catalyst surface and hinder the rate and lifetime of the catalyst. In the decarbonylation of furfural to furan, Pd has been shown to be an excellent catalyst for the reaction in both the liquid and vapor phases. The challenge of this chemistry has been deactivation of the catalyst from fouling reactions that are thought to proceed primarily through acid catalyzed oligomerization. Basic buffers have been added to the catalyst either as surface treatments (vapor phase) or as solid materials added to a liquid phase slurry reactor. Finding catalyst supports which enhance decarbonylation activity while minimizing deactivation reactions such as carbon fouling is important to the success of a Pd based process. Treating supports with basic buffers and base treatments has been shown to be effective in prior work, but a solid support that is active, stable and high temperature capable would have high value in this technology.
Supported palladium catalysts are known to catalyze furfural decarbonylation reaction with high selectivity but are limited by short lifetime. For example, U.S. Pat. No. 3,007,941 teaches a process for the production of furan from furfural comprising heating a liquid phase consisting essentially of furfural in the presence of palladium metal and a basic salt of an alkali metal; the basic salt is not part of the catalyst per se but is continuously added to the liquid phase during the reaction. Also, U.S. Pat. No. 3,257,417 a process for production of furan comprising contacting liquid furfural with a palladium catalyst in the presence of calcium acetate. Both these processes suffer from quick catalyst deactivation and difficult catalyst regeneration processes. U.S. Pat. No. 3,223,714 teaches a continuous low pressure vapor phase decarbonylation process for the production of furan comprising contacting furfural vapor with a supported palladium catalyst. A preferred catalyst has about 0.3 wt % Pd supported on alumina. The catalyst can be regenerated in situ but the lifetime of a running cycle for the catalyst is short and the production of furan per cycle is low. Catalysts which contain platinum and/or rhodium and to which cesium has been added are preferably used.
Co-pending U.S. Published Patent Application 2011/0196126 A1 hereby incorporated by reference in its entirety, provides a process for the vapor-phase decarbonylation of furfural to furan using heating a Pd/alumina catalyst that has been promoted with an alkali carbonate.
There remains a need for catalysts for the decarbonylation of furfural to furan with improved lifetime and high productivity.